A heat exchanger is a device for transmitting heat from a high temperature fluid to a low temperature fluid through a heat transfer wall, and is typically used in heaters, coolers, evaporators or condensers. Hereinbelow, an evaporator equipped with a heat exchanger will be described in detail.
An evaporator constitutes a refrigeration system (not shown) and works together with a compressor, a condenser and an expansion valve in the refrigeration system. In the operation of a refrigeration system, a low temperature and low pressure gas refrigerant from an evaporator is compressed by a compressor, thus becoming a compressed gas refrigerant having a high temperature and a high pressure. The high temperature and high pressure gas refrigerant flows into a condenser, in which the gas refrigerant is cooled by atmospheric air, thus becoming a low temperature and high pressure liquid refrigerant. The liquid refrigerant flows from the condenser into an expansion valve, in which the liquid refrigerant passes through small-sized holes so that the pressure and temperature of the liquid refrigerant are reduced. Thus, the low temperature and high pressure liquid refrigerant becomes a low temperature and low pressure liquid refrigerant in the expansion valve. Thereafter, the low temperature and low pressure liquid refrigerant flows through evaporation tubes of the evaporator and absorbs heat from the area surrounding the tubes, thus evaporating in the tubes so as to become a low temperature and low pressure gas refrigerant.
When hot room air is blown into the gaps between the low temperature refrigeration tubes of the evaporator by a blower during the above-mentioned process, heat is transferred from the air to the tubes, so that the air becomes cool air. Thus, the refrigeration system can cool the room by supplying the cool air into the room.
As shown in FIG. 1 and FIG. 2, a conventional evaporator comprises a core 10 with two connection pipes 70 connected at respective ends thereof to the core 10. The core 10 comprises an upper header tank 50 made of a longitudinal pipe having a large-sized cross-section, a lower header tank 20 having the same shape as the upper header tank 50 and placed beneath the upper header tank 50 such that they are parallel to each other, and a plurality of tubes 60 communicating with the upper header tank 50 at first ends thereof and with the lower header tank 20 at second ends thereof. Further, a plurality of corrugated fins 30 is continuously placed from the upper header tank 50 to the lower header tank 20 at locations between neighboring tubes 60.
During operation, the conventional evaporator having the above-mentioned construction absorbs a large amount of heat from the surroundings and the temperature of the surface of the core 10 is maintained at a point lower than that of the surroundings, so that the vapor around the core 10 is condensed on the surface of the core 10, thus forming condensed water. The condensed water formed on the surface of the core 10 is dropped downwards into a drain tray after passing by the lower header tank 20 due to gravity.
However, the evaporator having the above-mentioned construction is problematic as follows. When the evaporator stops operation, the condensed water cannot be completely drained downwards from the lower header tank 20, but some of the condensed water remains in a condensed water collection space 40, defined between the lower ends of the tubes 60, the fins 30 and the lower header tank 20, because the surface tension acting on the condensed water in the condensed water collection space 40 is greater than the force of gravity acting on the condensed water. In the above state, mold or germs may inhabit the condensed water remaining in the condensed water collection space 40, thus having an ill effect on the health of users and contributing to a reduction in the durability of the evaporator.